1. Field of the Invention
The present invention relates to a method for making a field emission display device, and more particularly to a method for making a carbon nanotube field emission display device.
2. Description of Prior Art
Carbon nanotubes are a novel carbonaceous material discovered by Iijima, a researcher of NEC corporation, in 1991. Relevant information was reported in an article by Iijima, entitled “Helical Microtubules of Graphitic Carbon” (Nature, Vol. 354, P56, 1991). Carbon nanotubes can transmit an extremely high electrical current and emit electrons easily at a very low voltage of less than 100 volts, which make it a very promising potential material for field emission applications.
Referring to FIG. 13, U.S. Pat. No. 6,232,706, invented by Hongjie Dai et al., discloses a field emission device using aligned parallel bundles of carbon nanotubes 100 extending from patterned catalyst layers 130 deposited on a layer of porous silicon 120 which is formed on a substrate 110 using a chemical vapor deposition (CVD) process. The carbon nanotubes produced by the CVD process have a variety of heights in a wide range so that the bundles of carbon nanotubes each forms a top which may be flat, concave, or in different pattern since the grown height is neither predictable nor controllable. Furthermore, a thin layer is formed on the top of the bundle which includes nanotubes with a variety of sizes, a number of remaining catalyst particles and amorphous carbon. These defects usually result in uniformity and unreliability of the field emission from the bundles of carbon nanotubes.
In order to optimize electron emissions, a triode-type field emission device is used. U.S. Pat. No. 6,515,415 discloses a typical triode-type field emission device, which generally includes a cathode electrode having carbon nanotube array emitters, an anode electrode with a phosphor screen, and a gate electrode positioned between the cathode electrode and the anode electrode to control emission of electrons from the carbon nanotube array emitters. The carbon nanotube arrays are usually produced using a chemical vapor deposition process.
In order to lower the emission turn-on voltage, a precisely controlled distance between the emitters and the gate electrode is required. Although the carbon nanotubes array growth higher with longer the reaction time, it is very difficult to control the growth height precisely. Therefore, the distance between the emitters and the gate electrodes is difficult to control merely by growth.